Some of the known existing floating covers consist of a thin and fragile membrane, of aluminum, secured to the top of pontoons which float on the surface of the liquid. This pontoon system leaves a 6" to 8" space between the surface of the liquid and the membrane, and this traps vapors in that space. Therefore, if a break or puncture of the membrane occurs, all these vapors are lost. Furthermore, aluminum does not resist the caustic and chloride environment which can be present in the tanks.
Another system consists of conventional steel pans floating on the surface of the liquid. This system was developed many years ago and is now outdated, because it is expensive, requires a long time for installation and is definitely sinkable. Apart from the above, its performance is further hampered in Northern climates.
Still another known system consists of an aluminum honeycomb type cover which floats on the liquid. However, aluminum does not offer any resistance to the caustic and chloride environment.